The present invention relates to films of improved conformability suitable for use as a label on deformable and/or irregular shaped articles (such as a squeezable plastic bottle or graphic art displays).
It is desirable to provide improved polymeric films which conform better to irregular surfaces to which the film may be applied for example when used as a facestock in the label or graphic art fields. Previous films which were highly conformable were often unsuitable for use as labels. To achieve improved levels of conformability required unacceptable compromises on other film properties also desired or necessary in a label. For example conformable labels had unacceptable optical properties e.g. insufficient clarity for a transparent label to achieve a “no-label look”.
Certain multi-layer polypropylene films which comprise layers of other copolymers are known.
For example WO 00/54968 (Mobil) describes a multi-layer film with a core layer of syndiotactic polypropylene. Other layers of the film (such as a skin layer and/or a layer adjacent to the core layer of this film) may comprise ethylene copolymers and/or terpolymers containing co-monomers of propylene and butene-1. These films are stated to have advantageous barrier properties for example for packaging applications. They are also described as having “remarkable toughness and resistance to deformation” which teaches directly away from use of such films on conformable substrates.
The present invention provides sheets which address some or all of the previously mentioned problems (for example with conformability) and are particularly suited for uses such as labelling squeezable articles.
Therefore broadly in accordance with the present invention there is provided a biaxially oriented polyolefin single or multi-layer film which comprises at least one core layer comprising a propylenic polymer component and either an ethylenic polymer component or a styrenic polymer component characterised in that the dynamic loss modulus (E″) of the film measured at 3 Hz and 25° C. is:    (a) from about 28 to about 136 MPa, preferably about 100 MPa measured in the transverse direction (TD); and/or    (b) from about 73 to about 135, preferably about 100 MPa measured in the machine direction (MD).
The films of the invention are suitable for use as a label on deformable substrates such as squeezable containers (e.g. plastic bottles). Labels of these films can conform with the substrate whilst retaining acceptable other properties. The films can exhibit reduced creasing and visual blemishes after repeated deformation yet can retain acceptable performances of other properties such as good optical performance desired for a transparent label film. The films can if desired be made with balanced properties and/or the core layer can be substantially free of additives which otherwise may have a detrimental effect on other film properties.
It is particularly surprising given the teaching of WO 00/54968 that films of the invention with ethylenic and/or styrenic polymer components have improved conformability.
Broadly in accordance with a further aspect of the present invention there is provided a biaxially oriented polyolefin single or multi-layer film which comprises at least one core layer comprising a propylenic polymer component and either an ethylenic polymer component or a styrenic polymer component characterised by a dynamic storage modulus (E′), measured at 3 Hz and 25° C. of:    (a) from about 630 to about 2800 MPa measured in the transverse direction (TD); and/or    (b) from about 1300 to about 3000 MPa measured in the machine direction (MD).
Optionally films of the invention have the values given herein for both dynamic loss modulus (E″) and for dynamic storage modulus (E′)
Broadly in accordance with a yet further aspect of the present invention there is provided a biaxially oriented polyolefin single or multi-layer film which comprises at least one core layer comprising a propylenic polymer component and either    (x) from about 0.2% to about 8% of an ethylenic polymer component; or    (y) from about 0.2% to about 25% of a styrenic polymer component; by weight of the core layer.
The ethylenic polymer component is preferred.
Preferably the films of the invention are substantially transparent and/or have other acceptable optical properties such as haze (wide or narrow angle) gloss etc, for use as a clear transparent label to produce a no-label look.
In a further aspect of the present invention there is provided a method of selecting those polymeric films which are of improved conformability suitable for labelling a deformable and/or irregular shaped article to having reduce blemishing thereon during use; the method comprising the steps of:    (a) preparing polymeric (preferably polyolefin) film comprising at least one core layer comprising a copolymer formed from at least propylene and ethylene monomers    (b) measuring at 3 Hz and 25° C. in the MD and/or the TD, the dynamic loss modulus (E″) and/or the dynamic storage modulus (E′) of the film;    (c) selecting those films for use in labelling (optionally as a label facestock) which have at least one of the following properties:            (i) E″ in the TD from about 20 to about 150 MPa;        (ii) E″ in the MD from about 70 to about 150 MPa;        (iii) E′ in the TD from about 600 to about 3000 MPa; and/or        (iv) E′ in the MD from about 1300 to about 3000 MPa.            (d) optionally applying a film selected from step (c) as a label to a squeezable article.
Conveniently films of and/or used in the present invention may exhibit the following values:    (i) E″ in the TD from about 28 to about 136 MPa;    (ii) E″ in the MD from about 73 to about 135 MPa;    (iii) E′ in the TD from about 630 to about 2800 MPa; and/or    (iv) E′ in the MD from about 1300 to about 3000 MPa.
More conveniently films of and/or used in the present invention exhibit the following values:    (i) E″ in the TD of from about 56 to about 124 MPa,    (ii) E″ in the MD of from about 76 to about 122 MPa,    (iii) E′ in the TD of from about 920 to about 2430 MPa, and/or    (iv) E′ in the MD of from about 1325 to about 2390 MPa.
Most conveniently films of and/or used in the present invention exhibit the following values:    (i) E″ in the TD of from about 80 to about 111 MPa,    (ii) E″ in the MD of from about 80 to about 108 MPa,    (iii) E′ in the TD of from about 1320 to about 2060 MPa, and/or    (iv) E′ in the MD of from about 1350 to about 2175 MPa.
Specific films which may be of and/or used in the present invention exhibit the following values:    E″ (TD)≈90 MPa; E″ (MD)≈94 MPa; E′ (TD)≈1360 MPa; & E′ (MD)≈1470 MPa;    E″ (TD)≈87 MPa; E″ (MD)≈89 MPa; E′ (TD)≈1280 MPa; & E′ (MD)≈1560 MPa; and/or    E″ (TD)≈84 MPa; E″ (MD)≈90 MPa; E′ (TD)≈1340 MPa; & E′ (MD)≈1580 MPa.